1. Field of the Invention
The present invention relates to an ignition coil apparatus for an internal combustion engine in which a plug boot is installed on a main body of the internal combustion engine by being inserted into a bent plug hole.
2. Description of the Related Art
In the past, there has been known an internal combustion engine in which a plug hole is bent at its intermediate portion due to the complication of a cylinder head upper structure, the compact formation of a cylinder head and combustion chambers, and the adoption of a structure to arrange a multitude of spark plugs in a single cylinder to fire a mixture therein.
When an ignition coil apparatus for an internal combustion engine (hereinafter abbreviated as an “ignition coil”) is installed on a main body of the internal combustion engine by inserting a plug boot into such a bent plug hole, for the purpose of preventing a reduction in the insertability or insertion property of the plug boot, for example, an ignition coil as described in a first patent document (Japanese patent application laid-open No. H5-52175) employs a bendable coil spring that is arranged between a first metal fitting and a second metal fitting in the flexible plug boot so as to bend an intermediate portion thereof.
However, in the ignition coil described in the above-mentioned first patent document, provision is required for the first metal fitting, the second metal fitting and the coil spring so as to bend the intermediate portion of the plug boot, thus posing a problem that the number of component parts required is increased and the production cost becomes high.
In addition, in the ignition coil having the plug boot molded with its intermediate portion being bent, there is also a problem that molding processing of the bent hollow plug boot is difficult.